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Continuing with the tetrahedral theme, observe that the 4 vertices of a regular tetrahedron are such that every three of them form an equilateral triangle.

How many points in 3-space can you find so that every three of them form an isosceles triangle?(Note: An equilateral triangle counts as isosceles.)© Copyright 1996 Stan Wagon. Reproduced with permission.

2 October 1998